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Measuring the glycemic index of foods: interlaboratory study

2008; Elsevier BV; Volume: 87; Issue: 1 Linguagem: Inglês

10.1093/ajcn/87.1.247s

1938-3207

Thomas M.S. Wolever, Jennie Brand‐Miller, John Abernethy, Arne Astrup, Fiona Atkinson, Mette Axelsen, Inger Björck, Furio Brighenti, Rachel Brown, Audrey E. Brynes, Maria Cristina Casiraghi, Murielle Cazaubiel, Linda Dahlqvist, Elizabeth Delport, Gareth Denyer, Daniela Erba, Gary Frost, Yvonne Granfeldt, Shelagh M. Hampton, Valerie Hart, Katja A. Hätönen, Christiani Jeyakumar Henry, Steve Hertzler, Sarah Hull, Johann C. Jerling, Kelly L. Johnston, Helen Lightowler, Neil Mann, Linda Morgan, Leonora N. Panlasigui, Christine Pelkman, Tracy Perry, A. Pfeiffer, Marlien Pieters, D. Dan Ramdath, Rayna T Ramsingh, Sathyasurya Daniel Robert, Carol Robinson, Essi Sarkkinen, Francesca Scazzina, Dave Clark D. Sison, Birgitte Sloth, Jane Staniforth, Niina Tapola, Liisa Valsta, Inge Verkooijen, Martin O. Weickert, Antje R. Weseler, Paul Wilkie, Jian Zhang,

Diet and metabolism studies

Background: Many laboratories offer glycemic index (GI) services. Objective: We assessed the performance of the method used to measure GI. Design: The GI of cheese-puffs and fruit-leather (centrally provided) was measured in 28 laboratories (n = 311 subjects) by using the FAO/WHO method. The laboratories reported the results of their calculations and sent the raw data for recalculation centrally. Results: Values for the incremental area under the curve (AUC) reported by 54% of the laboratories differed from central calculations. Because of this and other differences in data analysis, 19% of reported food GI values differed by >5 units from those calculated centrally. GI values in individual subjects were unrelated to age, sex, ethnicity, body mass index, or AUC but were negatively related to within-individual variation (P = 0.033) expressed as the CV of the AUC for repeated reference food tests (refCV). The between-laboratory GI values (mean ± SD) for cheese-puffs and fruit-leather were 74.3 ± 10.5 and 33.2 ± 7.2, respectively. The mean laboratory GI was related to refCV (P = 0.003) and the type of restrictions on alcohol consumption before the test (P = 0.006, r2 = 0.509 for model). The within-laboratory SD of GI was related to refCV (P < 0.001), the glucose analysis method (P = 0.010), whether glucose measures were duplicated (P = 0.008), and restrictions on dinner the night before (P = 0.013, r2 = 0.810 for model). Conclusions: The between-laboratory SD of the GI values is ≈9. Standardized data analysis and low within-subject variation (refCV < 30%) are required for accuracy. The results suggest that common misconceptions exist about which factors do and do not need to be controlled to improve precision. Controlled studies and cost-benefit analyses are needed to optimize GI methodology. The trial was registered at clinicaltrials.gov as NCT00260858.